TPS should be 0% at idle. The screw in the throttle body is not used to set the idle speed, it's used to set the minimum idle air with the IAC disconnected. The idle speed is programmed into the PCM.

The fact that the minimum idle air screw is not making any contact with the "throttle body arm" and the TPS% is not 0% suggests the problem lies elsewhere. Specifically, I would clean the connection to the throttle position sensor (TPS) and see if that helps. With the engine off, but the key in the "Run" position, does the scanner still show the TPS value as >0%? If you push on the throttle body arm, can you force the value to go to 0%? If yes, it's possible the throttle blades or linkage is worn/binding. Also make sure no one tried to "slot" the holes on the TPS to make it adjustable. '90 and up ECM/PCMs self-zero the TPS unlike the earlier cars. If the TPS still shows >0% at idle, replace it with a known good TPS.

Once you get the idle to come down to where it should be, you can worry about resetting the minimum idle air.

 

my tps is slotted . it's a factory slotted tps. so if the 96 tps wasnt slotted then this one must be for 90 or earlier.
i'm going in the garage to check the tps and try what you suggested.
i'l be balk

 

1989 and earlier were slotted
1990 and later were not slotted
The '96 TPS will not interchange with the earlier slotted style TPSs(different connector style)
If someone hacked some slots into it, adjust it back to 0%. If it's a factory slotted sensor, it may be that someone hacked an ealier style throttle body onto your car.

 

it is a factory slotted tps. i looked at it close and its not a GM brand.
the throttle body on my motor is a 58mm tb, not a factory lt4 tb.
with the tps on the tb at wot it was @91% and with the motor off it was at 20.8% thats the lowest i could get it.when i start the car it goes higher to the upper 28-35%
i took it off and open it all the way and it went to 100% but only 20% fully closed. i moved it around with the motor running and it made no diff.
oh and the plug that goes to the tps .... someone cut the wires and spliced a plug onto the factory wires that fits the tps. the wires are thicker and diff colors than the original wires before the splice.
but why did it idle before @800 rpm

 

If this data was taken at idle I think you need to look at your ign advance. Its reading around a steady 43-44 and thats way to much for idle, should be arounf 13-14 degrees. Now if you are holding it at a different higher rpm that might account for the high ign advance which could be the source of the problem. ....G

 

Ok. Someone hacked it The fact that it'll go no lower than 20% says that the TPS is bad or the wiring to it is bad. Since this idle issue just started, it's likely the sensor. Based on your description, I'd say you have a late '80s TPS. As I recall, those are cheap...$35 or so....if you want to toss a new one on for grins.

When you were moving it around with the motor running, it'll have no affect on the idle speed, but it was affecting the injector pulse width. I bet the PCM was wondering what the h*ll was going on

 

jim, i went to advanced auto today to get a tps and when i opened the box i see why they put a diff tps on there. the one for a 96lt4 will not work on my 58mm tb its totally diff. so he got the part # off the one that was on my tb that i brought with me just incase and it takes one from a 85-89 chevy smallblock.
anyway i just put it together and it now shows 0% at idle and when i start it it idled at @850 and with the ac on about the same
so its fixed
i just want to thank you and everyone else for the help.its fixed just in time to get everything loaded up to leave tomorrow for the c4 gathering.
ohh, one more thing. where should i set the screw at. its not touching the tb arm right now.
i also am sending you a pm jim.

 

How many miles on your injectors? Mine had 96K on them with 2 of them stuck open. I removed all of them and shipped them to Witchhunter.com and for only $12.50 each, $15.00 if you have them tested with before and after results sent to you, my vette is running like new. No Kidding. If anything, it they should be cleaned and reconditioned as a preventive maintinance job. Good luck.

 

To set the minimum idle air, do the following:

- Turn the key to "Run" (don't start the engine)
- Unplug the connector at the IAC
- Turn the key to "Off" and then start the engine
- Adjust the set screw so that the engine will barely idle (generally this will be around 450-500 rpm)
- Turn the engine off
- Reconnect the IAC connector
- Start the engine and allow the engine to idle until the idle stops hunting.

If the engine idles as it currently exists, then it'll be fine. It's not unusual for the set screw on 58mm throttle bodies to not be touching the throttle body arm.

 

Replacing the front 02 sensors fixed the problem with the running rich condition, which was caused by one of the originals which were not reading correctly. Just replacing the O2 sensors does not completely resolve an O2 sensor problem however. After replacing O2 sensors, it is a good idea to disconnect battery voltage from the PCM for 10~30 seconds to clear its memory. When the bad sensor(s) were in the car, the PCM "learned bad habits" due to the erroneous O2 readings and saved some of that bad info in the Block Learn Multiplier (BLM) cells inside the PCM. By disconnecting the battey you cleared the PCM's bad "learned" values and it was forced to "re-learn" using the correct values from the new O2 sensors.

With the help of the others and especially the excellent suggestions by 96GS#007, you've fixed the O2 sensor problem and the high idle problem. Similar to the O2 sensor errors, the TPS sensor errors also threw the PCM's calculations off and caused the high idle. Now that you have the sensors replaced and the idle correctly adjusted, I would recommend disconnecting the battery one more time so that the PCM will again be forced to "re-learn" the operating parameters using the good values from the properly working TPS and O2 sensors. After reconnecting the battery, you should take the car for a drive and gently work it through its normal driving routine. Then you should be good to go.

 

Mike_88Z51, just gave some good advise. I would do this!!

 

thanks mike, i actually did have the battery disconnected for about 15-20 mins while in bowling green. i just got back and i am just reading this.
while i was in bowling green, the battery died and i bought a new optima in bowling green and had it disconnected for at least 15 min while we were triming the battery tray for the optima to fit down in the tray. the battery and the tps sensor was the only problems i had the whole time at the gathering. i got the tps wet cleaning the motor and it went bad so i bought a new one while i was there getting the battery and it hasnt gave me any problems since. perfect idle.

i did dyno it while at the gathering and the guys running the dyno said it had a misfire in the upper rpms and you can see it on the dyno chart. they think its ignition because the wide band o2 shows @ 12.6- 12.8 all the way thru. fuel pressure never dropped. all 3 runs were very consistant, only 2 hp diff on all 3 and 3 ft lbs on all 3 runs. it actually made more power on every run the 3rd made the most hp and tq.
393.5 hp and 398.8 tq. in the middle of a HOT day and thru the mufflers on pump gas. i couldnt spray it cause we couldnt find and nitrous in bowling green sat.
i did run ithard quite a few times thru the gears while there and i never heard or felt it misfire once. but after @ 5500 rpm the power and tq istarts jumping around on the chart. they said they heard it in the car while dynoing it.
its running perfect to me right now to me. i did have people tell me that it looked rich when i was on it. they were behind me following me on a cruise in bg.